1. Field of the Invention
The present invention relates generally to an image position correcting optical system and, more particularly, to an optical system incorporating a function to correct a fluctuation in an image position that is derived from a shake of a lens.
2. Related Background Art
In the present specification, a "correction of an image position" means correcting a fluctuation in the image position due to a shake or the like by displacing a certain lens unit in a direction across an optical axis.
In a conventional image position correcting optical system, as disclosed in the specification of U.S. Pat. No. 4,907,868, the number of lens elements constituting an image position correcting lens unit is as large as 4, enough to occupy a space that is elongate along the optical axis. As a result, there increases a size of a drive actuator for displacing the image position correcting lens unit in a direction substantially orthogonal to the optical axis.
Further, according to an image position correcting optical system disclosed in the specification of U.S. Pat. No. 4,978,205, the image position correcting lens unit is composed of three pieces of lens elements, but a secondary chromatic aberration is not compensated.
As explained above, the conventional image position correcting optical system presents such inconveniences that the image position correcting lens unit is constructed of a large number of lens elements, and the drive actuator of the image position correcting lens unit and, in turn, the optical system as a whole increase in size.
Also, if down-sizing is attained to some degree by reducing the number of lens elements constituting the image position correcting lens unit, the compensation of the secondary chromatic aberration is insufficient, resulting in such an inconvenience that an imaging performance is poor.